Ordinarily, in the mixing and application of cements and mortar, it is important to provide a setting time which is sufficiently long to enable the mix to be poured or cast into a form or a desired shape. The setting time of the mix is sufficiently long to also enable the cement or mortar to be finished to the desired surface finish or texture.
For certain specific end uses, however, these prior art cements and mortars are not useful because their setting and curing times are too long. Certain uses, particularly those involving overhead or out-of-position pouring or casting require cements or mortars having a relatively quick setting time.
When agents are added to increase the setting time of these cements, or when other fast setting materials are employed, there often is not enough time mix and pour the material before it begins to set.
One particular application requiring fast setting materials involves the securing of anchoring elements, such as rock bolts, in or to walls or other structures, and is commonly employed in mines. Since prior art inorganic cements set relatively slowly, mixtures of hardening organic resins or other fast setting materials have been used for securing these anchors into boreholes in the mine wall.
An early practice involved the pre-mixing of the components of the resin followed by introduction of the resin and the bolt into the borehole. After curing, the hardened resin would hold the bolt in the borehole. Later techniques involved the utilization of a dual compartment cartridge, with each compartment separately storing the reactive components of the organic resin. Then the cartridge would be inserted into a previously drilled hole, followed by insertion of a bar. The ramming of the bar into the hole would thus break the cartridge and allow the components of the resin to mix. Since the polyester resin formulation set very rapidly, it developed the necessary holding power in a matter of minutes.
Prior art patents in this field disclose two compartment cartridge systems with one compartment containing a resin and the other compartment containing a hardener component. The frangible cartridge is ruptured by the force of the insertion of the anchor element into the borehole with the resin and hardening material being mixed by mechanical action. Exemplary patents in this field include U.S. Pat. Nos. 3,861,522 (Llewellyn et al.); 3,430,449 (Novotny et al.); 3,705,646 (Jankowski et al.); 3,731,791 (Fourcade et al.) and 3,921,800 (Burns).
The anchoring cartridge system discussed above has several major disadvantages. Because it contains an organic resin, the cartridge is hazardous in that it not only supports combustion, but actually fuels combustion should a fire occur in the mine. Furthermore, the flammability of the resins would destroy the holding capacity of the anchor and would result in the failure of the anchor in the event of a fire. In addition, these cartridges are relatively expensive.
For these reasons, fast-setting cementitious compositions have been sought for such securing of anchoring elements. U.S. Pat. No. 3,108,443 describes a two-compartment cartridge wherein one compartment contains dry cement and the other compartment contains water. The components are designed to mix upon the breaking of the cartridge. Due to the slow setting of the mix, however, there is a great tendancy of the water to flow out of the borehole. Thus, uneven mixing results which in turn provides unsatisfactory holding power.
One method for curing this defect is disclosed by U.S. Pat. No. 4,096,944 (Simpson) wherein a hydraulic cement powder is enclosed in a frangible casing. A multitude of water containing microcapsules are uniformly dispersed throughout the cement powder. These microcapsules of water, however, are relatively difficult to produce and maintain in the cartridge.
Applicants have now discovered cement compositions which set and cure rapidly. When used in the above-described cartridges, these composition provide a suitable method for securing mine bolts to walls, ceilings and floors. In comparison to the Simpson patent, the present invention greatly simplifies the manufacture of the cartridge in that the micro-encapsulation of water is not required. The present invention also overcomes the disadvantages of prior art organic resin cartridges in that such composition are not flammable.